They stood at their prescribed posts, according to the Law of Moses the man of God. The priests splattered the blood, which they received from the hand of the Levites.
The time appointed for the passover having arrived, a very great congregation came together upon the occasion, Ch2 30:13. Now here we have, I. The preparation they made for the passover, and good preparation it was: They took away all the idolatrous altars that were found, not only in the temple, but in Jerusalem, Ch2 30:14. Before they kept the feast, they cast out this old leaven.
Commenting on 2 Chronicles 30:13-20
For there were many in the congregation that were not sanctified,.... Or purified from uncleanness, contracted either by idolatry, or through such things which, according to the ceremonial law, made them unclean, and from which they had not now time to cleanse themselves according to the law: therefore the Levites had the charge of the killing of the passovers for everyone that was not clean...
the priests sprinkled the blood, which they received of the hand of the Levites--This was a deviation from the established rules and practices in presenting the offerings of the temple. The reason was, that many present on the occasion having not sanctified themselves, the Levites slaughtered the paschal victims (see on Ch2 35:5) for everyone that was unclean.